Here'* a really good deal on an OBDI scan tool:
I bought this package and am well pleased with the performance and the value.
However, you will need to buy and modify your own OBDII cable to fit the '94 or "95 Bonneville. The '94 and '95 Bonneville use OBDI protocol in the PCM but use an OBDII DLC (data link connector) under the steering wheel. You can purchase the necessary OBDII short cable from Actron for about $15, cut it and rewire it as shown here, and it should work swell on your '94.
Whole deal ends up costing a little more than $105.
Also, read in above thread about a cable from Actron that is supposed to do the same thing made up nice and pretty by the factory for $40